It is known in the plastic film industry to blow compressed air adjacent to the edges of a hot film web to "fix" or pin the web at the edges in an attempt to reduce neck-in thereof. For example, Japanese Pat. No. 57-43816, dated Mar. 12, 1982, discloses the use of air nozzles located at two positions in the air gap range between a T-die and press roll to blow compressed air onto both ends of film extruded from the T-die. After the ends are fixed by the blown air the film is bonded onto a substrate by means of a press roll and cooling roll. The patent indicates that the amount of neck-in of the extruded film may be reduced.
Nylon Plastics, a book published by John Wylie & Sons, Inc. (1973), on page 250 thereof, discloses the use of copper tubing jets to prevent edge weaving and excessive neck-in of nylon film prior to contact with a chill roll.
The above-described arrangements would appear to be relatively ineffective insofar as attaining their desired results are concerned. In particular, each of the devices disclosed in the prior art incorporates nozzles which direct rather localized jets onto the surface of the moving film. Thus, puncture of the film or other damage thereto may result from the air jets exiting from the nozzles, particularly at the high air velocities which may be required to attain the desired objectives. In addition, there is no teaching in the prior art of any significant degree of entrainment of ambient air through use of these devices which target rather localized spots on the web.